Defect inspecting method and apparatus

ABSTRACT

A defect inspecting apparatus of the invention solves a problem that in a defect inspecting apparatus, because of improving detection sensitivity of a microscopic defect by reducing a detection pixel size, a focal depth becomes shallow, a height of imaging is varied due to environmental change and the detection sensitivity of a defect becomes unstable. This apparatus comprises an XY stage, which carries a substrate to be inspected and scans in a predetermined direction, and a mechanism having a system of irradiating a defect on the inspected substrate at a slant and detecting the defect by a detection optical system disposed on the upper side, which corrects a height of imaging in real time for change in temperature and barometric pressure in order to keep the imaging in a best condition.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/428,065, filed on Apr. 22, 2009, now U.S. Pat. No. 7,733,475, whichis a divisional of U.S. patent application Ser. No. 11/717,651, filed onMar. 14, 2007, now U.S. Pat. No. 7,535,561, claiming priority ofJapanese Patent Application No. 2006-068479, filed Mar. 14, 2006, theentire contents of each of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to an inspection method and inspectingapparatus, particularly to a technology suitable for inspecting thegeneration state of a defect such as a particle etc. in a manufacturingprocess by inspecting a defect such as a particle etc. produced in themanufacturing process for forming a pattern on a substrate tomanufacture an object, such as a semiconductor manufacturing process, aliquid display element manufacturing process, and a printed circuitboard manufacturing process, analyzing and taking measures.

In a semiconductor manufacturing process, a particle on a semiconductorsubstrate (wafer) may cause a failure such as an insulation failure orshot-circuit. Further, as semiconductor elements become miniaturized, ifa microscopic particle is present, the microscopic particle may cause aninsulation failure of a capacitor or breakdown of a gate oxide film.Such a particle comes to be mixed in, with taking various forms such asa particle produced from a moving part of a carrier device or a humanbody, a matter created by reaction of a process gas in a processingdevice, and a matter which is a chemical or a material mixing in.

Similarly, also in a liquid display element manufacturing process, ifadherence of a particle to a pattern formed on a substrate of a liquiddisplay element or any defects on the pattern occur, the substrate cannot be used as a display element. Also, the same goes for a printedcircuit board manufacturing process, and adherence of a particle maycause a short-circuit and insufficient connection on a pattern.

Conventionally, there is one technology, as disclosed in JP-A-62-89336,for detecting a particle on a semiconductor substrate of this type inwhich a laser beam is projected onto a semiconductor substrate to detectscattered light generated from a particle when the particle adheres tothe semiconductor substrate and the detected light is compared with theinspection result obtained the adjacent inspection of a semiconductorsubstrate of the same product class, which eliminates disinformationfrom patterns and enables highly-sensitive and highly-reliableinspection of a particle and defect. Further, as disclosed inJP-A-63-135848, there is a technology in that a laser beam is projectedonto a semiconductor substrate to detect scattered light generated froma particle when the particle adheres to the semiconductor substrate andthe detected particle is analyzed by an analyzing technology such aslaser photoluminescence or two dimension X-ray and Magnetic Resonanceimaging (XMR) analysis.

Further, for a technology of inspecting such a particle as the above, amethod is disclosed that a wafer is irradiated with coherent light anddiffracted light produced from a repeating pattern on the wafer isremoved by a spatial filter, thus the particle or defect withoutrepeatability is highlighted to be detected. Further, a particleinspecting device is disclosed in JP-A-1-117024 in which a circuitpattern formed on a wafer is irradiated from the direction tilted at 45°to a group of main straight lines on the same pattern to preventzero-order diffracted light from the group of main straight lines fromentering the opening of an objective lens. In JP-A-1-117024, it is alsodescribed that the other group of straight lines other than the mainstraight lines are light-shielded by a spatial filter. Further, aconventional technology concerning a defect inspecting apparatus of adefect such as a particle etc. and a method thereof is disclosed inJP-A-2000-105203 in that a detection pixel size is changed by switchinga detection optical system. A technology for measuring the size of aparticle is disclosed in JP-A-2001-60607 and No. 2001-264264.JP-A-2004-177284 discloses a technology for detecting a defect on a thinfilm in that a laser beam is narrowed down to form a beam spot which iselongated in the direction perpendicular to a stage moving direction,and detection is performed in the direction perpendicular to anillumination direction.

BRIEF SUMMARY OF THE INVENTION

In the cases of JP-A-63-135848, No. 1-117024 and No. 2000-105203, thedefect detection sensitivity fluctuates owing to changes in temperatureor barometric pressure at a location where the defect inspectingapparatus is installed and sensitivity calibration frequency tends toincrease due to the following reasons, improving deterioration in anoperating rate of the apparatus due to frequent calibration is achallenge.

To detect a microscopic defect in the process of a recent, miniaturizedsemiconductor, in a defect inspecting apparatus, the SN of a defectsignal strength is enhanced by reduction in a detection pixel size. Thereduction in the detection pixel size makes the focal depth of adetection optical system shallow, therefore the relative refractiveindex of a detection lens is changed and a body tube is expandedthermally owing to fine changes in temperature or barometric pressure,thus the height of imaging of a defect is displaced, accordingly theimage defocuses to decrease detection sensitivity. A clean room in whicha defect inspecting apparatus is installed often provides aninsufficient distance from adjacent equipment or a wall, and a localtemperature in the environment of installation may change in about anhour. Keeping the detection sensitivity needs sensitivity calibration,but more frequent calibration may lower the operating rate of theapparatus because one calibration requires several minutes. For measuresagainst it, there is a method of installing an apparatus in a dedicatedthermal chamber, but because of disadvantages that the apparatus may beexpensive and a footprint may be enlarged, this method is not suitablefor a defect inspecting apparatus. Further, on the one hand, becausebarometric pressure in a clean room is not controlled, the sensitivitymay become unstable when a low or high atmospheric pressure passes.

An object of the present invention is, to solve the above problems, toprovide a defect inspecting apparatus configured so that a height ofimaging can be corrected in real time for changes in temperature andbarometric pressure.

To achieve the above object, in the invention, a mechanism in which achange in temperature or barometric pressure decreases the sensitivitywas studied and measures against it were devised. More specifically, themechanism is such that temperature and barometric pressure at a locationof installation of the defect inspecting apparatus may have deviationfrom temperature and barometric pressure under which the sensitivity wasadjusted up to a maximum in the same conditions and accordingly a heightof imaging of a defect varies, and therefore measures are that a defectinspecting apparatus is provided which includes a construction forcorrecting the height of an object surface or image surface in real timefor a change in at least either temperature or barometric pressure sothat the image of an inspected substrate formed on an image sensor by adetection lens does not defocus. That is, a temperature of an inspectionlens and a barometric pressure near the inspection lens are measured anda height of imaging for correction, or a height of the inspectedsubstrate for correction when a sensor height is fixed, is derived fromtheir deviation values, then after correction, inspection is carriedout. The correction value is read out from a data table beforeinspection, which is created in advance from relation betweentemperature and barometric pressure, and the height of imaging, which isobtained in adjustment of the defect inspecting apparatus.

[Mechanism of Sensitivity Decrease Due to Change in Barometric Pressure]

A mechanism of the sensitivity decrease when barometric pressure fallsis as follows. When barometric pressure falls, air density becomes small(proportionality relation), and therefore a relative refractive index ofa detection lens becomes large and a focal length of the detection lensbecomes small. As the result, a height of imaging becomes small,resulting in defocus and decrease in sensitivity. When barometricpressure rises, a mechanism is opposite to the falling case, the heightof imaging becomes large, resulting in defocus and decrease insensitivity. The height of an inspected substrate in relation to changein barometric pressure will be described with reference to FIG. 3.Plotted in the figure are heights of the inspected substrate at whichthe image of a defect does not defocus when an image sensor is fixed andbarometric pressure in an apparatus changes. In the relation between thebarometric pressure and the heights of the inspected substrate, theheight of the inspected substrate changes linearly, because the relativerefractive index between air and a lens is a linear function ofbarometric pressure. A shift ΔZ of a height of imaging when barometricpressure changes will be described with reference to FIG. 4. In imagingrelation, an object surface is comprised of the inspected substrate 1, alens is comprised of an upper detection optical system 200 and animaging surface is comprised of an image sensor 205, and when barometricpressure rises, a focal length of the lens becomes large. Therefore,when a height of the image sensor is fixed, the height of the inspectedsubstrate 1 may be lowered by −ΔZ to bring focus on the image sensor. Onthe contrary, when the inspected substrate 1 is fixed, it is necessaryto raise the height of the image sensor by a longitudinal magnificationof the detection lens, i.e. ΔZ×the magnification².

[Mechanism of Sensitivity Decrease Due to Change in Temperature]

A mechanism of sensitivity decrease when temperature falls is asfollows. When temperature falls, air density becomes large(proportionality relation), and therefore a relative refractive index ofa lens becomes small and a focal length becomes large. As the result, aheight of imaging becomes large, resulting in defocus and decrease insensitivity. When temperature rises, a mechanism is opposite to thefalling case, and the height of imaging becomes small to cause defocusof the image of a defect, resulting in sensitivity decrease. Inaddition, change in temperature has influence on elongation of adetection lens body tube, and the height of imaging variescomplicatedly. For example, when temperature falls, a length of the lensbody tube becomes small due to thermal expansion, and as the result,unless a position of the object surface is raised, the height of imagingdefocuses to decrease the sensitivity.

[Data about Relation Between Temperature and Barometric Pressure, and aHeight of an Object Surface or an Image Surface]

Using as a reference point standard environment which is regulated to,for example, 23° C. and 1,013 hPa and the height of an object surface oran image surface at which an image does not defocus under theenvironment, that is, the height of the object surface or the imagesurface having the maximal sensitivity under certain optical conditions,there is determined relation between barometric pressure and temperaturemeasurements with respect to the reference point and a deviation of theheight of the object surface or image surface at which imaging does notdefocus when an environmental temperature at a location of installationof a defect inspecting apparatus is changed in a positive manner inadjustment, or when the environment changes. A data table for it will bedescribed with reference to FIG. 5. Under the same optical conditions,i.e. the same detection magnification, the same illumination condition,the same substrate under test (a standard wafer for confirmingsensitivity) and when a temperature at the location of installation ofthe defect inspecting apparatus is changed by ±2° C., a height of theinspected substrate Z at which the maximal sensitivity (maximal signalstrength) may be obtained is found. The standard wafer for confirmingsensitivity may be desirably, for example, a substrate formed byapplying evenly particles of PSL uniform in size onto a siliconsubstrate. The height of the substrate Z is plotted by 1 μm a graph inwhich the ordinate axis represents barometric pressure and the abscissaaxis represents temperature. In this example, the height of thesubstrate Z is in the unit of 1 μm, but a focal depth of a detectionoptical system may be desirably used as a minimal unit.

Because barometric pressure is proportional to gas density owing to astate equation, the height of the substrate approximately conforms tosimulated data obtained from tracking a beam of light with barometricpressure being varied in an optical imaging simulator. Therefore, thesimulated data as shown in FIG. 3 may be desirably used as data tocreate the data shown in FIG. 5.

[Correction Method]

Since temperature and barometric pressure are measured before inspectionand a height of imaging or a position of an image sensor, i.e. acorrection value for a height of an object surface or image surfacecorresponding to the temperature and barometric pressure is read fromFIG. 5 to correct the height of the object surface or image surface toinspect, an operator can inspect not knowingly at a maximal sensitivityunder selected optical conditions. Needless to say, without using theabsolute data table in which the reference point is set as describedabove, it is also possible that a coefficient is derived in advance fromrelation between temperature and barometric pressure, and the height ofthe object surface or image surface, and then a correction value for theheight of the object surface or image surface may be computed andobtained relatively by multiplying a deviation between two points of thetemperature and barometric pressure with the coefficient.

More specifically, in a block diagram shown in FIG. 12, a control CPUportion 401 stores a Z coordinate (Z reference value) at which themaximal sensitivity is provided, a barometric pressure at that time(barometric pressure reference value), a temperature (temperaturereference value) at that time, a coefficient obtained in advance forconverting a barometric pressure into the Z coordinate (barometricpressure coefficient) and a coefficient for converting a temperatureinto the Z coordinate (temperature coefficient).

For correction of change in barometric pressure, a Z correction value isderived by adding a Z conversion value of barometric pressure for thechange to a variation to the Z reference value, which Z conversion valueis obtained by computing a difference between a measurement value by abarometric pressure measure 504 at an arbitrary time and the barometricpressure reference value and by multiplying it by the barometricpressure coefficient.

For correction of change in temperature, the Z correction value isderived by adding a Z conversion value of temperature for the change toa variation to the Z reference value, which Z conversion value isobtained by computing a difference between a measurement value by atemperature measure at an arbitrary time and the temperature referencevalue and by multiplying it by the temperature coefficient. Because thecorrection of change in barometric pressure and the correction of changein temperature function independently from each other, the Z correctionvalue may be obtained by adding both of the Z conversion value based onbarometric pressure and the Z conversion value based on temperature tothe Z reference value, and by this correction value, concurrentcorrection of barometric pressure and temperature can be performed. A Zstage control unit 305 can locate a height of the inspected substrate atwhich the maximal sensitivity is provided, by changing a height of the Zstage 303 by the Z correction value.

As described above, the invention enables highly-sensitive detection ofa defect wherein focal depth becomes shallow while stabilizing thesensitivity without lowering of the operating rate by calibration.

The invention is effective for change in the environment, and becausethe inspection lens and the environment change near the lens aremeasured, further countermeasures can be made against change in atemperature of an inspection lens caused by a local heat produced in theapparatus, such as a driving system of an inspection XY stage, a lightsource, sensors, controllers etc.

When the invention is applied, a thermostatic chamber is not required asmeasures for change in temperature, and therefore a size, cost andrequirement for environment of equipment can be reduced.

The above features and other features than the above of the inventionwill be now described hereinafter. Other objects, features andadvantages of the invention will become apparent from the followingdescription of embodiments of the invention in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is view illustrating system configuration of a defect inspectingapparatus.

FIG. 2 is a view illustrating the configuration of a system according tothe invention.

FIG. 3 is a graph showing relation between barometric pressure and theheight of an inspected substrate in focus.

FIG. 4 is a view explaining that the height of an inspected substrate isvaried by change in barometric pressure.

FIG. 5 is a graph of relation between temperature and barometricpressure and a correction amount for the height of an inspectedsubstrate.

FIG. 6 is a view for explanation of a spot formed by illuminating aprojection plane of an image sensor on an inspected substrate from threedirections.

FIG. 7 is a view illustrating an inspected substrate on which memoryLSIs, i.e. samples to be inspected, are arranged.

FIG. 8 is a view illustrating an inspected substrate on which LSIs suchas microcomputers etc., i.e. samples to be inspected, are arranged.

FIG. 9 is a view illustrating an optical system, including anillumination lens of an illumination optical system, of the defectinspecting apparatus according to the invention.

FIG. 10 is a view illustrating the function of the illumination lens ofthe illumination optical system in the defect inspecting apparatusaccording to the invention.

FIG. 11 is a view for explanation of an illumination optical system.

FIG. 12 is a schematic view illustrating the principle of the inventionthat the height of a Z stage is corrected by using a coefficient of aconversion formula.

DESCRIPTION OF REFERENCE CHARACTERS

-   1—Inspected Substrate (Wafer),-   2—Chip,-   3—Slit-Like Beam (Illumination Region),-   4—Detection Region of Image Sensor such as TDI Sensor,-   100—Illumination Optical System-   101—Laser Source,-   102—Concave Lens,-   103—Convex Lens,-   104—ND Filter,-   110—0-degree Illumination Beam Spot Imaging Portion-   120—45-degree Illumination Beam Spot Imaging Portion (direction 10),-   130—45-degree Illumination Beam Spot Imaging Portion (direction 11),-   200—Vertical Detection Optical System,-   201—Objective Lens (Detection Lens),-   202—Spatial Filter,-   203—Imaging Lens,-   204—Zoom Lens Group,-   205—One-Dimensional Detector such as TDI Sensor,-   206—Sensor Z Driving System,-   300—Stage System,-   301-304—XYZθ Stage,-   305—Stage Control,-   400—A Control System,-   401—Control CPU Portion,-   402—Signal Processing Portion,-   403—Display Portion,-   404—Input Portion,-   500—Oblique Detection System-   501—Automatic Focus Unit,-   502—Signal Processing Circuit,-   503—Temperature Measure,-   504—Barometric Pressure Measure.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention will be described hereinafter withreference to the drawings. In the following drawings, similar functionalportions are denoted by the same reference signs.

First, a substrate 1 to be inspected for a defect such as a particleetc. according to the invention will be described with reference toFIGS. 7 and 8. Since the details are described in Japanese Patent No.3566589, the summary will be provided.

The substrate 1 to be inspected for a defect such as a particle etc. maybe, as shown in FIG. 7, a semiconductor wafer 1 a on which chips 1 aacomprised of memory LSIs are arrayed two-dimensionally at predeterminedintervals. The chip 1 aa comprised of the memory LSI is mainly formedwith a memory cell region 1 ab, a peripheral circuit region 1 accomprised of a decoder, a control circuit and the like, and anotherregion 1 ad. The memory cell region 1 ab is formed by arraying(repeatedly) a memory cell pattern two-dimensionally and regularly.However, the peripheral circuit region 1 ac is formed by arraying apattern two-dimensionally, but not regularly and repeatedly.

The substrate 1 to be inspected for a defect such as a particle etc. maybe, as shown in FIG. 8, a semiconductor wafer 1 b on which chips 1 bacomprised of LSIs such as microcomputers etc. are arrayedtwo-dimensionally at predetermined intervals. The chip 1 ba comprised ofthe LSI such as a microcomputer etc. is mainly formed of a registergroup region 1 bb, a memory region 1 bc, a CPU core region 1 bd and aninput/output region 1 be. Incidentally, FIG. 8 conceptually shows thearray of the memory region 1 bc, the CPU core region 1 bd and theinput/output region 1 be. The register group region 1 bb and the memoryregion 1 bc are formed by arranging patterns two-dimensionally andregularly (repeatedly). The CPU core region 1 bd and the input/outputregion 1 be are formed by arranging nonrepeating patterns. As describedabove, as for the inspected substrate 1 to be inspected for a defectsuch as a particle etc., even when a semiconductor wafer is addressed,although the chips are arranged regularly, in the chip, a minimal linewidth is different in each region, and further it is considered thatthere may be various arrangements such as a repeating patter,nonrepeating pattern and the like.

The defect inspecting apparatus of a particle etc. and a method thereofaccording to the invention are based on an apparatus that in such aninspected substrate 1 as above, zero-order diffracted light producedfrom a pattern (linear pattern) comprised of a group of lines on anonrepeating pattern region in the chip is blocked to enter an entrancepupil of an objective lens and scattered light produced by a defect suchas a particle etc. present on the nonrepeating pattern region isreceived, thereby allowing a signal caused from the defect such as aparticle etc. to be detected and a position coordinate of the defect tobe computed. The details are described for instance in Japanese PatentNo. 3566589 (particularly, see paragraphs 0033 to 0036), and here theexplanation will be omitted.

Next, a first embodiment of the defect inspecting apparatus according tothe invention will be described with reference to FIG. 1.

The first embodiment of the defect inspecting apparatus includes: astage portion 300 composed of an X stage 301, Y stage 302, Z stage 303capable of focusing on a surface of an inspected substrate, theta (θ)stage 304 and stage controller 305; a laser source 101; a concave lens102; and a convex lens 103. The apparatus further includes: anillumination optical system 100 comprising a beam expander, a beamformation portion composed of an optical filter group 104 and a mirror105, and three sets of a beam spot imaging portion composed of atransparent glass plate and a switchable optical branching element (or amirror) 106, an illumination lens with a cylindrical curved surface 107and mirrors 108, 109; a detection optical system comprising a detectionlens 201, a spatial filter 202, an imaging lens 203, a zoom lens group204 and a one-dimensional sensor (image sensor) 205 such as TDI etc.; anoptical system 500 comprising a lens and a sensor for detection at a lowelevation angle; a control system 400 comprising a signal processingsystem 402 composed of an A/D conversion portion, a data memory whichmay be delayed, a difference processing circuit for obtaining adifference between signals of chips, a memory for storing temporarily adifference signal between the signals of the chips, a thresholdcomputation processing portion for setting a pattern threshold and acomparison circuit, an output means for storing a detection result of adefect such as a particle etc. and outputting the detection result of adefect, a computation processing system 401 for controlling driving of amotor etc., a coordinate and an image sensor, a display system 403, andan input system 404. The defect inspecting apparatus is on the systemthat a defect on the inspected substrate is illuminated at a slant, theinspected substrate which is mounted on the XY stage is scanned in apredetermined direction and light generated by the defect is received bythe detection optical system disposed on the upper side, and theapparatus is characterized by including a mechanism which corrects aheight of imaging in real time for change in temperature and barometricpressure so that an image does not defocus. The detection optical system200 disposed on the upper side described above can detect a moremicroscopic defect and a defect equal to or smaller than a limit valueof resolving power, by including a magnifying lens to receive scatteredlight from the defect with a high NA, and magnifying and projecting itwith a high magnification on the image sensor to inspect in a smallpixel size.

A unit according to the invention will be described using FIG. 2. Theunit includes: an automatic focus system 501 having a position sensorand an imaging light path of off-axis for projecting and receiving alight beam which dose not pass through a lens in the detection lens 201;a signal processing circuit 502; the X stage 301, the Z stage 303 as astage Z mechanism for controlling the height of the inspected substrateto correct the height of an object surface; the stage control system305; the image sensor 205; the image sensor Z-direction driving system206 as a Z mechanism for moving up and down the image sensor to correctthe height of imaging; the control CPU portion 401; a barometricpressure measure 504; and a temperature measure 503. The control CPUportion 401, the stage control system 305 and the signal processingcircuit 502 form a control system for converting a deviation of at leasteither temperature or barometric pressure into a correction value forthe position of an object surface or image surface and for locating theobject surface or image surface, and can drive the image sensorZ-direction driving system 206 or the Z stage 303 to correct the heightof the object surface or image surface in real time for change in atleast either temperature or barometric pressure so that an image of theinspected substrate formed on the image sensor by the detection lensdoes not defocus. As for measurement of temperature and barometricpressure, in order to reduce an error due to a gradient of temperatureand barometric pressure, it is desirable to attach a sensor portion sothat the inside or the surface of the detection lens 201 can bemeasured. A result measured by the barometric pressure measure 504 andthe temperature measure 503 is sent to the control CPU portion 401, acorrection value ΔZ is read out based on a data table prepared from thegraph of FIG. 5 described above, and then a command as an offset valueis sent to the signal processing circuit 502. The signal processingcircuit 502 drives the stage Z in a closed loop until the offset valuecorresponding to the correction value ΔZ is provided by the automaticfocus system 501. When the height of the inspected substrate iscorrected, a spot 3 of a separate illumination system is displacedseparately, and therefore it becomes necessary to have a function forcorrecting automatically the position of the spot 3 to the center.

In this embodiment, also by using the image sensor Z-direction drivingsystem 206 and by relatively moving a value of ΔZ×magnification², aheight of the image sensor 205 may be varied so that the image sensorcan be located at a height of imaging displaced due to temperature orbarometric pressure and imaging with no defocus can be obtained.Autofocusing illumination light is configured in a manner that it has anillumination path in a space which does not interfere with the detectionlens, and illuminates the inspected substrate to provide dark-fieldillumination, and reflected light provides an image on an oppositeposition sensor. The autofocusing system uses desirably a light sourcehaving a wideband wavelength for preventing the light from interferingwith a pattern of a particular film thickness on the inspected substrateto lower signal strength. On the one hand, the detection lens isdesigned to bring out an imaging performance to a diffraction limit at asingle, inspection illumination wavelength, and therefore when theautofocusing light path is designed to be shared with the detectionlens, the lens becomes expensive largely. Particularly, when a detectionillumination wavelength is short and has a large difference from anautofocusing illumination wavelength, it is difficult to design the lensand an off-axis specification may be desirably applied.

The three illumination optical systems 100 are configured in a mannerthat a light beam emitted from the laser source 101 passes through thebeam expander composed of the concave lens 102 and the convex lens 103,and through the illumination lens 107 having a cylindrical curvedsurface so that a slit-like beam 3 irradiates the substrate (wafer) 1 tobe inspected from three directions 10, 11 and 12 in a plane as shown inFIG. 6 with the longitudinal direction of the slit-like beam 3 facingthe array direction of the chips. The array direction of the chipscorresponds to a detection region 4 of the sensor. Incidentally, thereason why the slit-like beam 3 is used as the illumination light isthat a scan width large in the X direction is made large and inspectionof a defect such as a particle etc. is sped up. Further, the slit-likebeam 3 from the three directions 10, 11, 12 may irradiate the substrateselectively from one direction or two directions 10, 12 concurrently byswitching a beam splitter or the mirror 106 to a transparent glass plateof the same thickness. The longitudinal direction of the slit-like beam3 is turned toward the array direction of the chips with respect to theinspected substrate 1 and perpendicular to a scan direction Y of the Ystage 302. This allows simplifying comparison of a pixel signal betweenthe chips and facilitating computation of a position coordinate of adefect, thereby speeding up inspection of a defect such as a particleetc.

FIGS. 9, 10 show an illumination lens 104 having a circular cone shapeand a cylindrical curved surface. A manufacturing method etc. of theillumination lens 104 having the cylindrical curved surface is describedin detail, for example, in Japanese Patent No. 3566589 (particularly,see paragraphs 0027 and 0028) and it may be manufactured by the knownmethod. The illumination lens 104 of a circular cone shape is a lenshaving different focal lengths at positions in the longitudinaldirection of a cylindrical lens, which lengths are varied linearly. Withthis configuration, even when illumination is provided at a slant(having tilts φ1, α1) as shown in FIG. 10, the slit-like beam 3 narroweddown in the Y direction and collimated in the X direction can irradiate.That is, according to this illumination lens 104, illumination having acollimated light beam in the X direction can be provided at near φ1=45°,as shown in FIG. 9( a). Especially, as shown in FIG. 9( a), theslit-like beam 3 is collimated in the X direction, and accordingly adiffracted light pattern can be obtained from a circuit pattern having amain group of lines facing the X or Y direction and be light-shielded bythe spatial filter 202.

The illumination lens 104 having the cylindrical curved surface can formthe slit-like beam 3 shown in FIG. 10.

FIG. 11 is a plan view illustrating the illumination optical system 100having the three beam spot imaging portions in FIG. 1. A laser beamemitted from the laser source 101 is branched into two light paths by abranching optical element 110 such as a half mirror etc., and one of thebranched beams is reflected by mirrors 111, 112 and turned downward by amirror 113 to enter the concave lens 102, thereby providing anillumination beam from the direction 11, and the other beam progressesto a branching optical element 114 such as a half mirror etc. Onebranched by the branching optical element 114 is reflected by a mirror115 and turned downward by a mirror 117 to enter the concave lens 102,thereby providing an illumination beam from the direction 10, and theother is turned downward by a mirror 116 to enter the concave lens 102,providing an illumination beam from the direction 10. By the way,illumination only from the direction 11 can be provided by switching thebranching optical element 110 to a mirror element 118. Also,illumination only from the directions 10 and 12 can be provided byremoving the branching optical element 110 from the light path or byswitching it to a transparent optical element. Further, illuminationonly from for example, the direction 12 selected from the two directions10 and 12 can be provided by switching the branching optical element 114to a mirror element 119.

Besides, for the laser source 101, the third higher harmonic wave THG ofa high-power YAG laser with a wavelength of 355 nm may be used becauseof branching, but it is not necessarily limited to 355 nm. Also, thelaser source 101 is not necessarily of YAG THG. That is, the lasersource 101 may be another laser source such as an Ar laser, nitrogenlaser, He—Cd laser, excimer laser and the like.

The detection optical system 200 is configured in a manner that lightoutgoing from the wafer 1 is detected by using the detection lens(objective lens) 201, the spatial filter 202 for light-shielding aFourier transform image out of reflected, diffracted light from arepeating pattern, the imaging lens 203, and the one-dimensional sensor205 such as TDI etc. The spatial filter 202 is disposed at a height ofimaging in a spatial frequency region of the objective lens 201, i.e. aFourier transform (corresponding to a projecting pupil) in order tolight-shield the Fourier transform image out of the reflected,diffracted light from the repeating pattern. Here, an image of anillumination area 3 on the wafer 1 shown in FIG. 7 is formed on theimage sensor 205 by the object lens 201 and imaging lens 203constituting a relay lens. A light-receiving area of the one-dimensionalsensor 205 such as TDI etc. is denoted by 4.

When the inspected substrate 1 having the circuit patterns of variousforms formed thereon as described above is irradiated with the slit-likebeam 3, the reflected, diffracted light (or scattered light) isprojected from the surface of the wafer, the circuit patterns, and adefect such as a particle. This projected light is received by the imagesensor 205 through the detection lens 201, spatial filter 202 andimaging lens 203 and is converted photoelectrically. In illuminance(power) of light beam flux emitted from the illumination optical systemsuch as the laser source 101 etc., its dynamic range may be changed bycontrolling a ND filter 104 or laser power to change.

Further, the inspected substrate (wafer) 1 has to be inspected for aparticle or a defect, the residue after etching and the like intrudingin a concave portion between wires etc. However, because thenonrepeating pattern is present on the inspected substrate 1, in orderto prevent zero-order diffracted light from the nonrepeating patternfrom entering the objective lens 201, as described above, the substrate1 is irradiated with the slit-like beam 3 arranging its longitudinaldirection in the X direction from the directions 10, 12 which forms anangle of about 45° to the Y axis. This makes it difficult to irradiatethe concave portion sufficiently, because the wires etc. form convexportions and block the slit-like beam 3.

Then, since a wiring pattern is often formed in the perpendicular andparallel direction, the substrate 1 may be irradiated with the slit-likebeam 3 from the direction 11 parallel to the Y axis, which allows theconcave portion between wires etc. to be sufficiently irradiated.Particularly, a wiring pattern of a memory LSI is often a linear patternhaving a length of several mm, therefore illumination from thisdirection 11 may allow often inspection. Also, depending on a pattern,when in the direction of 90°, rotating the wafer by 90°, or setting theillumination direction to the X direction allows inspection.

Next, the spatial filter 202 will be described. The chip 2 includes arepeating pattern such as the memory cell region 1 ab in the memory LSI1 aa, the register group region 1 bb in the LSI 1 ba such as amicrocomputer etc., and the memory region 1 bc, and it is required tolight-shield a diffracted light pattern (diffraction interferencepattern) generated from this repeating pattern by the spatial filter202. In a word, a repeating pattern, nonrepeating pattern and absence ofa pattern are mixed on the chip 2 and moreover a line width is differentfrom each other. Therefore a light-shielding pattern of the spatialfilter 202 is usually set so that diffracted light from, for example, arepeating pattern which frequently appears is eliminated. Further, whena spatial filter 202 with a variable light-shielding pattern asdescribed in JP-A-5-218163 and No. 6-258239 is used, it may be changeddepending on a circuit pattern in the chip 2. Alternately, spatialfilters of different light-shielding patterns may be provided as thespatial filter 202, and they may be switched depending on a circuitpattern in the chip 2. However, when the slit-like beam 3 is emittedfrom the direction 11, it becomes necessary to light-shield zero orderdiffracted light by the spatial filter 202 to eliminate it. At thistime, it is also obviously possible to light-shield high-orderdiffracted light to eliminate it by the spatial filter 202. As above,the eliminating method of diffracted light has been described in thecase of the repeating or nonrepeating pattern present in the chip 2 onthe inspected substrate 1.

Next, description will be made on detection sensitivity adjustmentcorresponding to the size of a defect such as a particle to be detected.When a detection pixel size of the one-dimensional sensor (image sensor)205 such as TDI etc. above the inspected substrate 1 is made small,although the throughput drops, improvement of the detection sensitivitymay be expected. Consequently, when a defect such as a particle smallerthan about 0.1 μm is to be detected, the detection optical system 200may be changed to a system in which a pixel size is made smaller. Morespecifically, three kinds of detection optical system 200 may beprovided, in which concerning the pixel size of the image sensor etc.,an image size on the wafer 1 is made variable. A realization method ofthis configuration is that the lens groups 204 are switched. At thistime, a configuration of the lenses may be designed so that a light pathlength from the wafer 1 to the one-dimensional sensor 205 such as TDIetc. needs not to be changed. Also, when such a design is difficult, inaddition to switching the lenses, a mechanism for changing a distance tothe image sensor may be used. Further, image sensors having differentpixel sizes in themselves may be switched.

It will be apparent to those skilled in the art that although theforgoing description has been made on the embodiments of the invention,the invention is not limited thereto, and various changes andmodifications may be made within the sprit of the invention and thescope of the appended claims.

The invention claimed is:
 1. A method for detecting a defect of asubstrate, the method comprising steps of: irradiating the substratewith a first light; detecting a second light from the substrate andforming an image of an illuminated area on the substrate; measuring anenvironment of a defect inspecting apparatus, wherein said environmentincludes a temperature and barometric pressure; and while inspecting thesubstrate, changing at least one of a height of a surface of thesubstrate and a height of a surface of the image based on a table,wherein said table is used for converting at least one of a deviationfrom a standard height of a standard substrate surface relative to achange of said environment, and a deviation from a standard height of animage surface relative to change of said environment.
 2. The methodaccording to claim 1, the changing step comprising: correcting aposition of an image sensor involved in forming the image.
 3. The methodaccording to claim 1, the changing step comprising: changing a height ofthe substrate.
 4. A defect inspecting apparatus comprising: anilluminating unit which irradiates a substrate with a first light; adetection unit which detects a second light from the substrate and formsan image of an illuminated area on the substrate; a plurality ofmeasurement units which measure an environment of the defect inspectingapparatus, wherein said environment includes a temperature andbarometric pressure; and a correcting unit which changes at least one ofa height of a surface of the substrate and a height of a surface of theimage, wherein: said correcting unit uses a deviation of saidenvironment, and a plurality of coefficients, and said coefficients areacquired by at least one of a relationship between said environment anda height of said surface of the substrate, and a relationship betweensaid environment and said image surface.
 5. A method for detecting adefect of a substrate, the method comprising steps of: illuminating thesubstrate with a first light; detecting a second light from thesubstrate; forming an image of an illuminated area on the substrate;measuring an environment, wherein said environment includes atemperature and barometric pressure; and changing at least one of aheight of a surface of the substrate and a height of a surface of theimage, wherein: during said changing step, a deviation of saidenvironment and a plurality of coefficients are used, and saidcoefficients are acquired by at least one of a relationship between saidenvironment and a height of said surface of the substrate, and arelationship between said environment and said image surface.